Funds are requested for the purchase of an Aviv model 62DS circular dichroism spectrometer. This instrument will be shared by a major user group consisting of members of several departments at Duke University. The proposed instrument will be equipped with accessories to enhance its effectiveness for the proposed applications. These include structure and stability studies of the following systems: 1. Designed proteins 2. Protein subdomains 3. Model protein folding intermediates 4. RNA enzymes 5. Human carbonic anhydrase II 6. Glycoproteins 7. Lectins 8. Membrane-associated proteins 9. Nucleic acids 10. Nucleic acid binding proteins The proposed instrument will also be used as a calibration source in the development of a prototype lifetime-resolved fluorescence-detected CD instrument. The Aviv CD spectrometer will replace an obsolete Jobin-Yvon instrument that is incapable of performing most of the experiments listed above. The features that make the Aviv spectrometer uniquely suited to our needs include: a Cary double-prism monochromator; a temperature-stabilized photoelastic modulator; well-documented software; a multiple-cell thermoelectric sample holder; automatic sample titration; and a light scattering accessory for collecting spectra of scattering samples. A growing number of projects at Duke have become structurally-oriented and the availability of the proposed instrument would make a significant contribution to the progress of these studies.